https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
class com.google.common.graph.DirectedGraphConnections$2 extends java.util.AbstractSet<N>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.google.common.graph.DirectedGraphConnections$2
  super_class: java.util.AbstractSet
{
  final com.google.common.graph.DirectedGraphConnections this$0;
    descriptor: Lcom/google/common/graph/DirectedGraphConnections;
    flags: (0x1010) ACC_FINAL, ACC_SYNTHETIC

  void <init>(com.google.common.graph.DirectedGraphConnections);
    descriptor: (Lcom/google/common/graph/DirectedGraphConnections;)V
    flags: (0x0000) 
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.graph.DirectedGraphConnections$2 this
         0: .line 137
            aload 0 /* this */
            aload 1
            putfield com.google.common.graph.DirectedGraphConnections$2.this$0:Lcom/google/common/graph/DirectedGraphConnections;
            aload 0 /* this */
            invokespecial java.util.AbstractSet.<init>:()V
            return
        end local 0 // com.google.common.graph.DirectedGraphConnections$2 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/graph/DirectedGraphConnections$2;
    MethodParameters:
        Name  Flags
      this$0  final

  public com.google.common.collect.UnmodifiableIterator<N> iterator();
    descriptor: ()Lcom/google/common/collect/UnmodifiableIterator;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=4, locals=2, args_size=1
        start local 0 // com.google.common.graph.DirectedGraphConnections$2 this
         0: .line 140
            aload 0 /* this */
            getfield com.google.common.graph.DirectedGraphConnections$2.this$0:Lcom/google/common/graph/DirectedGraphConnections;
            getfield com.google.common.graph.DirectedGraphConnections.adjacentNodeValues:Ljava/util/Map;
            invokeinterface java.util.Map.entrySet:()Ljava/util/Set;
            invokeinterface java.util.Set.iterator:()Ljava/util/Iterator;
            astore 1 /* entries */
        start local 1 // java.util.Iterator entries
         1: .line 141
            new com.google.common.graph.DirectedGraphConnections$2$1
            dup
            aload 0 /* this */
            aload 1 /* entries */
            invokespecial com.google.common.graph.DirectedGraphConnections$2$1.<init>:(Lcom/google/common/graph/DirectedGraphConnections$2;Ljava/util/Iterator;)V
            areturn
        end local 1 // java.util.Iterator entries
        end local 0 // com.google.common.graph.DirectedGraphConnections$2 this
      LocalVariableTable:
        Start  End  Slot     Name  Signature
            0    2     0     this  Lcom/google/common/graph/DirectedGraphConnections$2;
            1    2     1  entries  Ljava/util/Iterator<Ljava/util/Map$Entry<TN;Ljava/lang/Object;>;>;
    Signature: ()Lcom/google/common/collect/UnmodifiableIterator<TN;>;

  public int size();
    descriptor: ()I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // com.google.common.graph.DirectedGraphConnections$2 this
         0: .line 157
            aload 0 /* this */
            getfield com.google.common.graph.DirectedGraphConnections$2.this$0:Lcom/google/common/graph/DirectedGraphConnections;
            getfield com.google.common.graph.DirectedGraphConnections.successorCount:I
            ireturn
        end local 0 // com.google.common.graph.DirectedGraphConnections$2 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/graph/DirectedGraphConnections$2;

  public boolean contains(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Z
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
        start local 0 // com.google.common.graph.DirectedGraphConnections$2 this
        start local 1 // java.lang.Object obj
         0: .line 162
            aload 0 /* this */
            getfield com.google.common.graph.DirectedGraphConnections$2.this$0:Lcom/google/common/graph/DirectedGraphConnections;
            getfield com.google.common.graph.DirectedGraphConnections.adjacentNodeValues:Ljava/util/Map;
            aload 1 /* obj */
            invokeinterface java.util.Map.get:(Ljava/lang/Object;)Ljava/lang/Object;
            invokestatic com.google.common.graph.DirectedGraphConnections.isSuccessor:(Ljava/lang/Object;)Z
            ireturn
        end local 1 // java.lang.Object obj
        end local 0 // com.google.common.graph.DirectedGraphConnections$2 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lcom/google/common/graph/DirectedGraphConnections$2;
            0    1     1   obj  Ljava/lang/Object;
    RuntimeVisibleTypeAnnotations: 
      METHOD_FORMAL_PARAMETER
        org.checkerframework.checker.nullness.qual.Nullable()
    MethodParameters:
      Name  Flags
      obj   

  public java.util.Iterator iterator();
    descriptor: ()Ljava/util/Iterator;
    flags: (0x1041) ACC_PUBLIC, ACC_BRIDGE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: .line 1
            aload 0
            invokevirtual com.google.common.graph.DirectedGraphConnections$2.iterator:()Lcom/google/common/collect/UnmodifiableIterator;
            areturn
      LocalVariableTable:
        Start  End  Slot  Name  Signature
}
Signature: Ljava/util/AbstractSet<TN;>;
SourceFile: "DirectedGraphConnections.java"
EnclosingMethod: com.google.common.graph.DirectedGraphConnections.successors:()Ljava/util/Set;
NestHost: com.google.common.graph.DirectedGraphConnections
InnerClasses:
  com.google.common.graph.DirectedGraphConnections$2
  com.google.common.graph.DirectedGraphConnections$2$1
  public abstract Entry = java.util.Map$Entry of java.util.Map